Everything this has been deduced from a framework called VoiceProvider. A framework is a set of instructions that serve as the basis for the development of new software, in this case and based on the name they have given it, it is supposed to develop a new tone for Siri. The idea that runs about this is that these new voices developed by third parties could be downloaded from the App Store as if it were an app.
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The benefits of this are several. Siri will be able to start handling languages and dialects that are currently beyond your knowledge, and would allow further customization of the assistant's voice, Who wouldn't like Siri to speak to him in George Clooney's voice, for example?
In any case this framework is in early stages of development so little can be known about him right now. What is speculated is that it could make its appearance at some point throughout the use of iOS and iPadOS 14.
This has been one of the numerous leaks that have taken place these days, and that have exposed many unknown details to form iOS and iPadOS 14. It seems that the next version of Apple's mobile system will come loaded with news, so now we can only wait for it to launch.